[Effect of Rotation of the Femoral and Tibial Components on Patellofemoral Malalignment in Knee Arthroplasty]

Patellofemoral complications are among the most common causes for revision surgery in total knee arthroplasty. So far no quantitative assessment has been made of the femoral and tibial malalignment or the positioning of the patellar component and the type of patellofemoral complication or failure. In particular, no comparative studies are available that include patients with and without patellofemoral failure in respect to the above-mentioned parameters when implant material, implant design, and fixation technique were identical. Between 1985 and 1992, 171 MG I total knee arthroplasties were performed. Since 1999, 20% of all the implanted MG I knee arthroplasties (all with metal-backed patellar component) had to be revised. Of those 34 patients, 18 were pair matched with 18 control patients based on the criteria of sex, body mass index, and age. The only difference in the control group was that they did not suffer any malfunction of the patellofemoral mechanism. To assess the patella component localization, conventional AP radiographs, patellar merchant view radiographs in 30 degrees, and CT scans were performed. This study has demonstrated a significant difference for the thickness of the patellar component and a trend regarding the rotational malalignment of the tibial component. Potential causes for the malrotation and guidelines to prevent rotational malalignment are discussed.